The present invention, in some embodiments thereof, relates to microRNAs and, more particularly, but not exclusively, to the use of same or alteration of same for generation of plants with enhanced resistance to abiotic stress.
MicroRNAs (miRNAs) are small, endogenous RNAs that regulate gene expression in plants and animals. In plants, they are processed from stem-loop regions of long primary transcripts by a Dicer-like enzyme and are loaded into silencing complexes, where they generally direct cleavage of complementary mRNAs. Although plant miRNAs have some conserved functions extending beyond development, the importance of miRNA-directed gene regulation during plant development is now becoming clear. mRNAs are already known to play numerous crucial roles at each major stage of development, typically at the core of gene regulatory networks, targeting genes that are themselves regulators. So far, microRNAs have been found to be involved in plant development, regulation of abiotic and biotic stress responses and hormone signaling (Jones-Rhoades et al., 2006, Ann Rev Plant Biol 57:19-53).
A commonly-used approach in identifying the function of novel genes is through loss-of-function mutant screening. In many cases, functional redundancy exists between genes that are members of the same family. When this happens, a mutation in one gene member might have a reduced or even non-existing phenotype and the mutant lines might not be identified in the screening.
Using microRNAs, multiple members of the same gene family can be silenced simultaneously, giving rise to much more intense phenotypes. This approach is also superior to RNA interference (RNAi) techniques, in which typically 100-800 by fragments of the gene of interest form a fold-back structure when expressed. These long fold-back RNAs form many different small RNAs and prediction of small RNA targets other than the perfectly complementary intended targets is therefore very difficult. MicroRNAs, in contrast, are produced from precursors, which are normally processed such that preferentially one single, stable small RNA is generated, thus significantly minimizing the “off-target” effect.
A second approach to functional screening is through over-expression of genes of interest and testing for their phenotypes. In many cases, attempting to over-express a gene which is under microRNA regulation results in no significant increase in the gene transcript. This can be overcome either by expressing a microRNA-resistant version of the gene or by down-regulating the microRNA itself.
Abiotic stress refers to such conditions as water deficit or drought, heat, cold, high or low nutrient or salt levels, and high or low light levels. In particular, drought and salinity are serious problems in agriculture and result in annual yield losses of billions of dollars worldwide. Many genes are involved in the responses to abiotic stress to in plants, but there is only limited information on miRNAs involved in plant response and adaptation to abiotic stress.
With a growing world population, increasing demand for food, fuel and fiber, and a changing climate, agriculture faces unprecedented challenges. In any given year, large areas of cornfields in the United States may be affected by at least moderate drought. Farmers are seeking advanced, biotechnology-based solutions to enable them to obtain stable high yields and give them the potential to reduce irrigation costs or to grow crops in areas where potable water is a limiting factor.